EP 0 193 012 A2 discloses a printing press and method for moving printing cylinders between thrown-off positions in which bearers connected with the cylinders are separated and thrown-on or placed in printing positions. The printing cylinders are urged into thrown-off positions by springs, which in one embodiment of the invention apply a biasing force to pivotally mounted support screws for the cylinders. In another embodiment the cylinders are mounted on cantilevered leaf springs which urge the cylinders towards their thrown-off positions. A motor is provided to apply a force directly to one of the printing cylinders to move it from its thrown-off position to its printing position. The other printing cylinders are moved from their thrown-off positions to their printing positions under the influence of forces transmitted between bearers connected with the printing cylinders.
EP 0 625 423 A1 corresponding to U.S. Pat. No. 5,301,609 discloses a printing unit with skew and throw-off mechanisms. A printing unit includes a frame, first and second brackets, and upper and lower plate cylinders. The first bracket is supported on the frame for movement relative to the frame. The upper plate cylinder has an end supported to move with the first bracket. The second bracket also is supported on the frame for movement relative to the frame, and the lower plate cylinder has an end supported to move with the second bracket. The printing unit also includes a skewing mechanism and a throw-off mechanism. The skewing mechanism moves the brackets transversely relative to the frame independently of each other. The throw-off mechanism pivots the brackets relative to the frame. The throw-off mechanism includes a pressure cylinder and a piston rod connected between the two brackets. The pressure cylinder and the piston rod are pivotally connected to the brackets and move pivotally relative to the brackets when the brackets are moved transversely by the skewing mechanism. The throw-off mechanism thus permits the brackets to be skewed independently of each other, while remaining connected with each other for throw-off.
Pending U.S. patent application Ser. No. 09/103,710 discloses an offset printing press for printing on a web. The press includes a frame, a first plate cylinder movably mounted in the frame, and a first blanket cylinder in selective contact with the first plate cylinder. A second blanket cylinder for forming a nip with the first blanket cylinder is in contact with a second plate cylinder. The press has a first operative condition, wherein the first plate cylinder and the first blanket cylinder are in direct contact with each other when double sided printing on the web is performed. In a second operative condition, the first plate cylinder and first blanket cylinder are separated to permit plates on the first cylinder to be changed while the second plate cylinder and the second blanket cylinder are printing on the web.
Different versions of impression setting are encountered in the technical field related to rotary printing presses. Various throw-off assemblies for bearered printing presses have been publically disclosed for many years, for example throw-off assemblies in various product lines that press manufacturers have long made available. The existing methods of setting impressions are time consuming, difficult to gauge or accurately tune, and require expensive assemblies. To set the desired impression, particularly the bearer squeeze, for each nip in the impression area, existing publically known designs require an operator to rotate a large, eccentric bearing housing by manually adjusting a turnbuckle mechanism or the like. The amount of squeeze attained is very sensitive to the turnbuckle's adjustment. There is no simple method of measuring the resulting impression setting. The eccentric bearing housings used with this method tend to both wear unacceptably over the time and bind in the side frames during adjustment. Due to the unavoidable wear of components, the impression assemblies require periodic readjustment in the field which imposes an unavoidable downtime on the respective printing press.
Separate mechanisms are required both to set the impression and to throw the cylinders off impression. This adds both cost and complexity to the assembly. There are no provisions to separate the blanket cylinders while leaving the plates in contact. Such a feature would allow the printing plates to be changed with the webs still in place.
During normal operation of the machine it is at times necessary to cock each of the plate cylinders with respect to the adjacent blanket cylinder by displacing one end of the plate cylinders. In the existing designs this relative angular motion results in a significant change in impression setting at the movable end of the respective cylinders.
In the past, various attempts have been undertaken to eliminate these deficiencies outlined above. Bearing housings with very small eccentrics have been linked to finely threaded turnbuckles in an attempt to desensitize the adjustment. The resulting, large mechanical advantage tended to make the assemblies self-locking. However when a broken web wrapped the printing cylinders the adjustments would not move or yield, potentially resulting in permanent damage to the printing cylinders. To minimize the binding and the wear at the frame housing interface, the thickness through the bores was increased and complex lubrication assemblies were introduced. This was only partially effective and added significantly to the costs of the respective assemblies.